Up to now, as electrophotographic photoreceptors, inorganic photosensitive materials such as amorphous selenium, selenium alloys, cadmium sulfide and zinc oxide and organic photosensitive materials represented by polyvinylcarbazole and polyvinylcarbazole derivatives have been widely known.
It is common knowledge that amorphous selenium or selenium alloys have superior characteristics and have been put into practical use. However, a complicated vacuum metallizing or deposition process is necessary for their production and further the vacuum-deposited film obtained has a drawback in that it lacks flexibility. Zinc oxide is used as a dispersed photosensitive material in which zinc oxide is dispersed in a resin, but it is disadvantageous in that the resulting photographic material has unsatisfactory mechanical strength and cannot be used repeatedly as is.
Polyvinylcarbazoles, well known as organic photoconductive materials, are advantages in that they have transparency, processability and film-formability. However, they have no photosensitivity in themselves in the visible ray region, and cannot be used practically as is. Accordingly, various sensitization methods have been provided. The spectral sensitization of polyvinylcarbazole using a sensitizing dye can expand its spectral sensitivity to the visible ray region. However, a sufficient photosensitivity for use as a electrophotographic photoreceptor is not obtained, and they have a drawback in that photo-fatique is remarkable.
On the other hand, spectral sensitization with an electron acceptor gives rise to electrophotographic photoreceptors having sufficient photosensitivity, and some of them have been practically used. However, there are still some problems with mechanical strength and durability.
Extensive research has been conducted on organic dispersed photosensitive materials, and there are many reports. However, electrophotographic photo-receptors having a superior electric characteristic and a sufficient photosensitivity have not been obtained yet. At present, there are reports about phthalocyanines which show superior electrophotographic characteristics for use as dispersed photosensitive materials. However, their spectral sensitivity is partial to the long wavelength region, and they have a drawback in that reproduction of red color is inferior.